The present invention relates to an anti-slipping agent for a frozen road surface and a spreading method thereof and more particularly to an anti-slipping agent for a frozen road surface to increase the friction between tires of vehicle and a road surface by spreading it onto a road surface covered with snow or a frozen surface, and to a method for spreading it. The present invention further relates to an apparatus for spreading the anti-slipping agent for a frozen road surface onto the road surface.
On roads in winter, a slippery road surface state (skid number: about 20) and a significantly slippery road surface state (skid number: 10-0) frequently occur under a variety of conditions. From the viewpoint of the maintenance of road surfaces in winter, therefore, efforts are being made to ensure traffic safety, by setting a target of the road surface state at skid numbers of 30 or larger. FIG. 1 is a schematic diagram showing the relationship among the road surface state, running speed of vehicles and skid number. The range shown by A is a state of road surface having ice sheet or ice film thereon, and the range shown by B is a state of road surface having compressed snow or grainy snow thereon. And the range shown by C is a state of pavement surface in wet conditions, and the range shown by D a state of pavement surface in dry conditions. The symbol xe2x80x9caxe2x80x9d corresponds to a sliding friction coefficient represented by skid number 30, xe2x80x9cbxe2x80x9d a sliding friction coefficient represented by skid number 20, xe2x80x9ccxe2x80x9d a sliding friction coefficient represented by skid number 10, xe2x80x9cdxe2x80x9d a sliding friction coefficient represented by skid number 0.
The most important measures to improve skid number are to prevent snow and/or ice from remaining on road surfaces. In order to carry out snow removal thoroughly, therefore, the usage of snowplow, the spreading of anti-freezing agents, sand, or the like for slip prevention, the roughening of frozen road surfaces by specialized instruments etc. are being executed as measures to improve skid number. However, sufficient results have not been obtained.
For example, materials used as anti-freezing agents, for the most part, consist of calcium chloride and sodium chloride (so-called salts). These salts used as anti-freezing agents, as well as sands for anti-slipping are both prone to fly away beyond roads when spread, depending on their specific gravity or particle diameter. After being spread onto a road surface, therefore, they are further whirled up by traveling vehicles without fixing to the road surface, and thus their slip prevention effect is hard to be maintained for a long time. In a case where a salt is employed, when the temperature of aqueous solution of the salt drops, the solution refreezes and renders a road surface to an ice board, which readily causes traffic failures. Furthermore, since a large amount of salt is usually used, there are growing apprehensions of the occurring of salt damage to environment and vehicles, and of environmental pollution.
For spreading of sand for anti-slipping, natural sand or crushed sand of stone is typically used. Even if an anti-slipping agent such as these natural sand or crushed sand of stone is spread onto a frozen road surface, however, they are whirled up by traveling vehicles and readily flies away to the roadsides or beyond the road. This creates a problem that their slip prevention effects cannot be retained for a long period of time. For example, if about a hundred vehicles pass on a road surface with an anti-slipping agent spread thereon, then a considerable amount of the anti-slipping agent frequently flies away and loses its slip prevention effect in about one to two hours. This results in an inconvenience that the use frequency and/or the spread quantity of anti-slipping agent must be increased to ensure traffic safety.
Accordingly, it is an object of the present invention to overcome the above-mentioned drawbacks associated with the conventional methods, that is, that neither of salts and sands are so high in the slip prevention effect on road surfaces in winter and that secondary failures such as the refreezing of aqueous solution of the salt used take place. It is another object of the present invention to eliminate any pollution by salt damage and improve the fixing property of an anti-slipping agent spread onto a frozen road surface, thereby retaining its slip prevention effect for a long period of time.
A first embodiment of the present invention is an anti-slipping agent composed of flat-crushed pieces obtained by crushing a stone having flat-crushability such as black slate as a raw material into small particles with increased flatness, through taking advantage of their flat-crushability. Since the crushed pieces of this anti-slipping agent for a frozen road surface are flat and have relatively high specific gravity (approximately 2.7), they can be spread unfailingly onto a road surface without flying away while being spread. When spread, therefore, the anti-slipping agent has a higher road covering efficiency per unit weight. Since it contacts the road surface closely and stabilizes, i.e., it has a good fixing property; its slip prevention effect can be retained for a long period of time.
A second embodiment of the present invention is a method for heating and spreading the anti-slipping agent for a frozen road surface. Because larger particles of the anti-slipping agent have higher heat capacities and smaller particles have lower heat capacities, when fixing to a road surface covered with snow and/or ice, the anti-slipping agent melts the snowy and/or icy road surface and quickly forms irregularities thereon, for improving the slip prevention effect.
Furthermore, a third embodiment of the present invention is an apparatus for spreading an anti-slipping agent for a frozen road surface, comprising: a hopper into which the anti-slipping agent is charged, heating means for heating the anti-slipping agent, and spreading means for spreading diffusely the heated anti-slipping agent onto a road surface. By this anti-slipping agent spreading apparatus in accordance with the present invention, the anti-slipping agent for a frozen road surface can be heated from about 100xc2x0 C. and then spread onto the frozen road surface.
As mentioned above, within this heated anti-slipping agent for a frozen road surface, the heat capacity varies according to the size of particle of the anti-slipping agent for a frozen road surface. When particles of the anti-slipping agent for a frozen road surface that have different heat capacities are spread on the frozen road surface, irregularities are formed on the frozen road surface that is being melted. Therefore, the slip prevention effect of the anti-slipping agent for a frozen road surface itself that has fixed to the road surface, and the frozen road surface having irregularities formed by anti-slipping agent, allows in combination the slip prevention effect to be retained for a long period of time and to be improved.